U.S. patent application number 09/841615 was filed with the patent office on 2002-01-31 for fluoropolymers.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Coggio, William D., Grootaert, Werner M.A., Hintzer, Klaus, Kolb, Robert E., Lohr, Gernot.
Application Number | 20020013438 09/841615 |
Document ID | / |
Family ID | 25285304 |
Filed Date | 2002-01-31 |
United States Patent
Application |
20020013438 |
Kind Code |
A1 |
Grootaert, Werner M.A. ; et
al. |
January 31, 2002 |
Fluoropolymers
Abstract
Curable fluoroelastomer compositions having improved compression
set after curing are provided, as well as compositions that are of
relatively high purity. These compositions include a
hydrogen-containing fluoroelastomer having interpolymerized units
derived from a cure-site monomer, a curative (optionally with a
co-agent), and an organo-onium. When the fluoroelastomer contains
units derived from vinylidene fluoride, the composition is
essentially free from an inorganic acid acceptor. Methods of
improving the compression of cured fluoroelastomer and cured
fluoroelastomers having improved compression set are also
provided.
Inventors: |
Grootaert, Werner M.A.;
(Oakdale, MN) ; Coggio, William D.; (Kastl,
DE) ; Hintzer, Klaus; (Woodbury, MN) ; Kolb,
Robert E.; (Afton, MN) ; Lohr, Gernot;
(Burgkirchen, DE) |
Correspondence
Address: |
Attention: James V. Lilly
Office of Intellectual Property Counsel
3M Innovative Properties Company
P.O. Box 33427
St. Paul
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
25285304 |
Appl. No.: |
09/841615 |
Filed: |
April 24, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09841615 |
Apr 24, 2001 |
|
|
|
09495600 |
Feb 1, 2000 |
|
|
|
Current U.S.
Class: |
526/242 |
Current CPC
Class: |
C08K 5/14 20130101; C08F
14/18 20130101; C08L 27/18 20130101; C08L 2205/02 20130101; C08F
14/18 20130101; C08K 5/00 20130101; C08F 6/22 20130101; C08L 27/12
20130101; C08F 6/22 20130101; C08L 27/12 20130101; C09D 127/18
20130101; C08K 5/49 20130101; C08K 5/14 20130101; C08K 5/17
20130101; C08L 27/18 20130101; C09K 3/1009 20130101; C08K 5/50
20130101; C08L 2666/04 20130101; C08K 5/36 20130101; C08L 27/12
20130101; C08L 2666/04 20130101; C08L 27/12 20130101; C08F 2/16
20130101 |
Class at
Publication: |
526/242 |
International
Class: |
C08F 214/18; C08F
012/20 |
Claims
What is claimed is:
1. A curable fluoropolymer composition comprising: a) a
hydrogen-containing fluoroelastomer having units derived from a
cure-site monomer, wherein the fluoroelastomer is capable of
peroxide cure; b) a peroxide curative; c) optionally, a co-agent
for the curative; and d) a non-fluorine-containing organo-onium;
with the proviso that when the hydrogen-containing fluoroelastomer
includes one or more units derived from vinylidene fluoride, the
composition is essentially free from one or more inorganic acid
acceptors.
2. The curable composition according to claim 1 wherein the
fluoroelastomer is essentially free of one or more units derived
from vinylidene fluoride.
3. The curable composition according to claim 2 wherein the
composition is essentially free from one or more inorganic acid
acceptors.
4. The curable composition according to claim 2 wherein the
composition includes an inorganic acid acceptor.
5. The curable composition according to claim 1 wherein the
fluoroelastomer includes one or more units derived from vinylidene
fluoride.
6. The curable composition according to claim I wherein the
fluoroelastomer further comprises pendant nitrile groups.
7. The curable composition according to claim 6 wherein the
curative comprises an ammonia-generating compound.
8. The composition according to claim 1 further comprising a
partially crystalline fluoropolymer.
9. A process for improving compression set of a cured
fluoroelastomer comprising: a. providing a curable fluoroelastomer
composition comprising: (i) a fluoroelastomer having units derived
from at least one monomer comprising a carbon-bonded hydrogen and
units derived from a cure-site monomer, wherein the fluoroelastomer
is capable of peroxide cure; (ii) a peroxide curative; (iii)
optionally, a co-agent for the curative; and (iv) a
non-fluorine-containing organo-onium with the proviso that when the
hydrogen-containing fluoroelastomer includes one or more units
derived from vinylidene fluoride, the composition is essentially
free from one or more inorganic acid acceptors; and b. curing the
curable composition.
10. The process according to claim 9 wherein the fluoroelastomer is
essentially free of one or more units derived from vinylidene
fluoride.
11. The process according to claim 9 wherein the composition is
essentially free from one or more inorganic acid acceptors.
12. The process according to claim 10 wherein the composition
includes an inorganic acid acceptor.
13. The process according to claim 9 wherein the fluoroelastomer
includes one or more units derived from vinylidene fluoride.
14. The process according to claim 9 wherein the fluoroelastomer
further comprises pendant nitrile groups.
15. The process according to claim 14 wherein the curative
comprises an ammonia generating compound.
16. A cured article comprising the composition of claim 1.
17. A cured article made according to the process of claim 9.
18. A cured fluoroelastomer comprising the reaction product of a
curable composition comprising: a) a hydrogen-containing
fluoroelastomer having units derived from a cure-site monomer,
wherein the fluoroelastomer is capable of peroxide cure; b) a
peroxide curative; c) optionally, a co-agent for the curative; and
d) a non-fluorine-containing organo-onium; with the proviso that
when the hydrogen-containing fluoroelastomer includes one or more
units derived from vinylidene fluoride, the composition is
essentially free from one or more inorganic acid acceptors.
19. The cured fluoroelastomer according to claim 18 having improved
compression set relative to the same cured fluoroelastomer made
without the organo-onium.
Description
[0001] This application is a continuation-in-part of U.S.
application Ser. No. 09/495,600, filed Feb. 1, 2000, now
pending.
FIELD OF THE INVENTION
[0002] The present invention relates to fluoropolymers, especially
elastomeric fluoropolymers (i.e., fluoroelastomers), compositions
incorporating such fluoropolymers, articles employing such
fluoropolymers, and methods of making and using such
fluoropolymers.
BACKGROUND
[0003] Cured compositions containing fluoropolymers are desirable
for a number of applications. For example, they can be used as
gaskets and O-rings. Such shaped articles having good compression
set (i.e., little or no deformation of the cured article after a
load is applied and removed) are particularly desirable.
[0004] Also, high purity fluoropolymers are used in a number of
industries. They are especially preferred for use in the
electronic, semiconductor, optical, medical, and pharmaceutical
industries, to name a few. These polymers have a relatively low
level of water extractable metals and metal compounds.
[0005] Inorganic acid acceptors are often added to fluoroelastomers
utilizing peroxide cure systems. Optionally, at least one metal
compound selected from divalent metal oxides or divalent metal
hydroxides is frequently blended with the fluoroelastomer during
preparation or before it is cured. While the presence of such
compounds improves the heat aging resistance and thermal stability
of the polymer (see, for example, U.S. Pat. No. 5,077,359), the
addition of such acid acceptors has a very detrimental effect on
the content of ions and extractables of the resulting elastomer
composition. EP Pat. No. B-708 797 discloses the use of
peroxide-curable fluoroelastomers with a fluoropolymer micropowder
filler for semiconductor applications. There is no disclosure of
how the materials were purified; however, due to the fact that this
process requires acid acceptors the overall ion content seems to be
unsatisfactorily high. Other fluoroelastomers that include such
inorganic acid acceptors include EP 0 140 207 and U.S. Pat. Nos.
4,233,421 and 4,912,171, for example.
SUMMARY OF THE INVENTION
[0006] The present invention provides curable fluoroelastomer
compositions, cured compositions, which can be secured to (e.g.,
coated on) a substrate, cured articles (e.g., shaped articles), and
methods. Preferably, the compositions of the present invention are
particularly useful as shaped articles such as gaskets and O-rings.
In certain aspects of the invention, the fluoroelastomer
compositions have improved compression set after being cured. In
certain other aspects of the invention, the fluoroelastomer
compositions are of a relatively high purity.
[0007] Preferably, the curable fluoroelastomer compositions of the
present invention have improved compression set after they are
cured. These curable compositions include a fluoroelastomer having
units derived from a cure-site monomer and capable of peroxide
cure, a peroxide curative for the fluoroelastomer, optionally a
co-agent for the curative, and a non-fluorine-containing
organo-onium. The improvement in compression set can be
demonstrated by a comparison of cured fluoroelastomers with and
without the organo-onium present. Those fluoroelastomers that
contain the organo-onium have surprisingly better compression set
properties than those of a similar or the same fluoropolymer
composition but not employing the organo-onium. That is, there is
little or no deformation of the cured article after a load is
applied and removed using the test procedure described in the
Examples Section when the fluoroelastomers are made using an
organo-onium compared to when they are not. Preferably, the
curative used in this embodiment is a peroxide.
[0008] This improvement is believed to be achieved whether or not
the fluoroelastomer is of relatively high purity, although high
purity can be desirable. Thus, in one aspect, the present invention
provides a relatively high purity polymer that is essentially free
of inorganic acid acceptors, which are typically bases such as
oxides and hydroxides of calcium, magnesium, zinc, lead, etc. In an
alternative embodiment, a relatively high purity polymer is
essentially free of all ions other than NH.sub.4.sup.+, H.sup.+,
and OH.sup.-. In these embodiments, the fluoroelastomer includes
one or more units derived from a hydrogen-containing monomer and
one or more units derived from a cure-site monomer. When the
hydrogen-containing monomer is a vinylidene fluoride, the curable
fluoroelastomer composition is essentially free from one or more
inorganic acid acceptors. The preferred high purity elastomeric
fluoropolymer is a peroxide-curable elastomer, optionally having
pendant nitrile groups.
[0009] In one embodiment, the present invention provides a curable
fluoropolymer composition that includes: a hydrogen-containing
fluoroelastomer having units derived from a cure-site monomer,
wherein the fluoroelastomer is capable of peroxide cure; a peroxide
curative; optionally, a co-agent for the curative; and a
non-fluorine-containing organo-onium; with the proviso that when
the hydrogen-containing fluoroelastomer includes one or more units
derived from vinylidene fluoride, the composition is essentially
free from one or more inorganic acid acceptors.
[0010] In another embodiment, the present invention provides a
process for improving compression set of a cured fluoroelastomer.
The method includes providing a curable fluoroelastomer composition
and curing the curable composition. The curable fluoroelastomer
composition includes: a fluoroelastomer having units derived from
at least one monomer including a carbon-bonded hydrogen and units
derived from a cure-site monomer, wherein the fluoroelastomer is
capable of peroxide cure; a peroxide curative; optionally, a
co-agent for the curative; and a non-fluorine-containing
organo-onium; with the proviso that when the hydrogen-containing
fluoroelastomer includes one or more units derived from vinylidene
fluoride, the composition is essentially free from one or more
inorganic acid acceptors.
[0011] In yet another embodiment, the present invention provides a
cured fluoroelastomer that includes the reaction product of a
curable composition including: a hydrogen-containing
fluoroelastomer having units derived from a cure-site monomer,
wherein the fluoroelastomer is capable of peroxide cure; a peroxide
curative; optionally, a co-agent for the curative; and a
non-fluorine-containing organo-onium; with the proviso that when
the hydrogen-containing fluoroelastomer includes one or more units
derived from vinylidene fluoride, the composition is essentially
free from one or more inorganic acid acceptors.
[0012] As used herein, the terms "a," "an," "the," "one or more,"
and "at least one" are used interchangeably.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0013] The present invention provides curable fluoropolymer
compositions that include a hydrogen-containing fluoroelastomer
having units derived from a cure-site monomer, a curative, and an
organo-onium. Optionally, the compositions can include a co-agent
for the curative and a partially crystalline fluoropolymer (e.g.,
fluorothermoplast or other fluoropolymer such as
polytetrafluoroethylene) as a filler. Certain embodiments of the
present invention are directed to polymers that have improved
compression set and certain embodiments of the present invention
are directed to polymers that have relatively high purity (i.e.,
polymers that are essentially free of ions other than
NH.sub.4.sup.+, H.sup.+, and OH.sup.- and/or essentially free of
inorganic acid acceptors).
[0014] The cured fluoroelastomer preferably has improved
compression set relative to the same cured fluoroelastomer made
without the organo-onium. Herein, an "improvement" is a decrease in
the residual deformation reported as a percentage compression set
as determined by the test method described in the Examples Section.
Preferably, the compression set is less than about 20%, more
preferably, less than about 15%, even more preferably, less than
about 10%, and most preferably, zero.
[0015] In cases where improved compression set is desired, the
addition of organo-onium compounds are beneficial to improve
properties in formulations that do not contain inorganic acid
acceptors; however, the improvement in compression set may be
achieved in the fluoroelastomers even if they are not essentially
free of inorganic acid acceptors and ions different than
NH.sub.4.sup.+, H.sup.+ and OH.sup.-.
Fluoropolymers
[0016] The fluoroelastomers used in the invention are not
perfluorinated. That is, they include units derived from at least
one monomer with hydrogen bonded to a carbon atom such that they
are "hydrogen-containing." They include interpolymerized units
derived from a cure-site monomer. The fluoroelastomers may or may
not include one or more units derived from vinylidene fluoride.
Preferably, the fluoroelastomers are essentially free of units
derived from vinylidene fluoride. By "essentially free from units
derived from vinylidene fluoride" it is meant that the
fluoroelastomer contains less than 10%, preferably less than 5%,
more preferably 0%, by weight of such units. Furthermore, the
composition may or may not include one or more inorganic acid
acceptors. If the fluoroelastomer includes one or more units
derived from vinylidene fluoride, the composition is essentially
free from one or more inorganic acid acceptors.
[0017] The fluoropolymer (including flouroelastomers and
fluorothermoplasts), preferably a fluoroelastomer, is typically a
polymerized product of one or more fluoroolefin monomers and
optionally one or more hydrocarbon olefin monomers. Generally, the
fluoroolefin monomers have from 2 to 8 carbon atoms. Examples of
such fluoroolefin monomers include tetrafluoroethylene (TFE),
vinylidene fluoride (VF.sub.2), hexafluoropropylene (HFP),
trifluoroethylene, chlorotrifluoroethylene (CTFE) and fluorinated
ethers such as perfluoroalkyl vinyl ethers (VE). Examples of useful
hydrocarbon olefins include ethylene and/or propylene.
[0018] The fluoropolymers are also derived from a cure-site
monomer. Examples of useful "cure site monomers" include bromine,
iodine, or nitrile groups, which can provide "cure sites" for
curing the fluoropolymer.
[0019] In case of peroxide-curable fluoroelastomers,
bromine-containing cure site comonomers are preferred such as a
bromine-containing olefin, preferably containing another halogen
such as fluorine. Examples are bromotrifluoroethylene,
4-bromo-3,3,4,4-tetrafluorobutene-1 and a number of others noted in
U.S. Pat. No. 4, 035,565. Brominated fluorovinyl ethers useful in
the invention include CF.sub.2Br--R.sub.f--O--CF.dbd.CF.- sub.2,
wherein R.sub.f is a fully fluorinated alkylene of up to 4 carbons
atoms like --CF.sub.2--, such as
CF.sub.2BrCF.sub.2OCF.dbd.CF.sub.2, cited in U.S. Pat. No.
4,745,165 and of the type ROCF.dbd.CFBr or ROCBr.dbd.CF.sub.2 where
R is a lower alkyl group or fluoroalkyl group each having up to 4
carbon atoms, such as CH.sub.3CF.dbd.CFBr or
CF.sub.3CH.sub.2OCF.dbd.CFBr, cited in U.S. Pat. No. 4,564,662. The
choice of bromine-containing units is based on copolymerizability
with the major monomers and low branching tendency, in addition to
cost and availability (U.S. Pat. No. 5,077,359).
[0020] Nitrile-containing cure site monomers may also be used.
Preferred examples are nitrile-containing fluorinated olefins and
nitrile-containing fluorinated vinyl ethers, such as
CF.sub.2.dbd.CFO(CF.sub.2).sub.mCN,
CF.sub.2.dbd.CFO[CF.sub.2CF(CF.sub.3)-
O].sub.q(CF.sub.2O).sub.sCF(CF.sub.3)CN,
CF.sub.2.dbd.CF[OCF.sub.2CF(CF.su- b.3)].sub.rO(CF.sub.2).sub.tCN,
where, in reference to the above formulaes m=2 to 12, q=0 to 4, r=1
to 2, s=0 to 6 and t=1 to 4. Representative examples of such a
monomer include perfluoro(8-cyano-5-methyl-3,6-dioxa-1- -octene),
CF.sub.2.dbd.CFO(CF.sub.2).sub.5CN, CF.sub.2.dbd.CFO(CF.sub.2).s-
ub.3OCF(CF.sub.3)CN,
CF.sub.2.dbd.CF--O--(CF.sub.2).sub.4--O--CF(CF.sub.3)- CN, and
CF.sub.2.dbd.CF--O--(CF.sub.2).sub.3--CN.
[0021] The optional partially crystalline fluoropolymer can be used
as a filler. In contrast to amorphous fluoroelastomers, partially
crystalline fluoropolymers are polymers with melting points
(typically, from 100.degree. C. to 340.degree. C.). The partially
crystalline fluoropolymers used in the invention can be used in the
form of their dispersions, i.e., the mixtures of the
fluoroelastomers and fillers may be prepared by blending the
latexes of the materials. Such dispersions can contain low
molecular weight polytetrafluoroethyene (PTFE), the so-called
micropowders or waxes (as described in U.S. Pat. No. 3,956,000)
optionally modified with HFP and/or VE. The dispersions comprise
melt-processable copolymers of TFE and perfluoro(propyl-vinyl)
ether known as "PFA", melt processable copolymers of TFE and HFP,
which is known as "FEP", also partially crystalline polymers of TFE
and ethylene (ET), which is known as "ETFE", or TFE, HFP and
VF.sub.2, which is known as "THV". These copolymers are extensively
described in "Modern Fluoropolymers", High Performance Polymers for
Diverse Applications, edited by John Scheirs, John Wiley & Sons
(1997), especially pages 223-270, 301-310, and 373-396. Preferably,
the partially crystalline fluoropolymers used as fillers have
melting points higher than the processing temperature of the
mixture.
Highly Pure Fluoropolymer Compositions
[0022] One aspect of the invention provides curable fluoroelastomer
compositions and cured polymers that are preferably essentially
free of inorganic acid acceptors and salts from coagulation. As
used herein, "essentially free" means less than 1000 parts per
million (ppm), and preferably less than 500 ppm. Such curable
compositions and the resultant cured products have a relatively
high purity.
[0023] In another aspect of the invention, there is provided
curable compositions and cured products that are essentially free
of all water extractable ions other than NH.sub.4.sup.+, H.sup.+
and OH.sup.- and more preferably, essentially free of all water
extractable ions except H.sup.+ and OH.sup.-, which are typically
present in the latex as a result of the polymerization process.
Examples of such ions include perfluorooctanoate, sulfate,
chloride, fluoride, etc. As used in this context, "essentially
free" means that less than 1000 ppm, preferably less than 500 ppm,
anions and cations (other than NH.sub.4.sup.+, H.sup.+ and
OH.sup.-) are found in the fluoropolymer (before adding cure
chemicals and other ingredients). Such curable compositions and the
resultant cured products have a relatively high purity.
[0024] Typically, inorganic acid acceptors are not added to the
process, and thus do not need to be removed. Removal of ions can be
performed by dialysis, preferably, ion exchange. An ion exchange
process is disclosed in, e.g., U.S. Pat. Nos. 4,282,162 and
5,463,021 and DE-A-20 44 986. Other processes are disclosed in
WO-A-99/62830 and WO-A-99/62858. A detailed discussion of certain
purification processes is presented below.
[0025] A preferred process of manufacturing fluoroelastomer
compounds that are essentially free of ions includes: purifying an
aqueous fluoroelastomer latex (or a blend of aqueous
fluoroelastomer latex and a latex of a partially crystalline
fluoropolymer--if a fluoropolymer filler is required) by using
separately a cationic and subsequently an anionic exchange
treatment, or vice versa, and coagulating the purified latex by
using salt-free methods.
Preparation of Fluoropolymers
[0026] The fluoropolymers (e.g., fluoroelastomers and partially
crystalline fluoropolymers), preferably fluoroelastomers, can be
prepared by known methods, preferably, by an aqueous emulsion
polymerization process. In this process, an aqueous colloidal
dispersion (i.e., latex) is obtained by polymerizing fluorinated
monomers in an aqueous medium containing a relatively high amount
of fluorinated emulsifiers such as salts of perfluoro octanoic acid
and the like with mild agitation. This process is described in
detail in "Modem Fluoropolymers", High Performance Polymers for
Diverse Applications, edited by John Scheirs, John Wiley & Sons
(1997), especially pages 233-237.
[0027] Emulsion polymerization is to be distinguished from the
suspension polymerization process. The latter method uses little or
no emulsifier and requires vigorous agitation that results in a
granular product. Usually emulsion polymerization is carried out
within a pressure range of 5 bar to 30 bar (5.times.10.sup.5 to
3.times.10.sup.6 Pa) and within a temperature range of 5.degree. C.
to 100.degree. C. Generally, emulsion polymerization processes use
significant amounts of adjuvants, such as emulsifiers, initiators,
buffers, etc., although a preferred polymerization process includes
a minimum level of adjuvants like buffers (and preferably, no
buffer).
[0028] It is generally accepted that a prerequisite for an aqueous
emulsification is the use of a non-telogenic emulsifier (U.S. Pat.
No. 2,559,752). As noted above, fluorinated emulsifiers, most often
perfluorinated alkanoic acids, are used. Generally, they are used
in an amount of from 0.02% by weight to 3% by weight with respect
to the polymer (i.e., based on the total weight of the
polymerizable composition).
[0029] A further material used in the polymerization process is a
water soluble initiator to start the polymerization. Commonly,
salts of peroxo-sulfuric acids are applied, often in the presence
of further co-agents like bisulfites or sulfinates (U.S. Pat. Nos.
5,285,002 and 5,378,782) or the sodium salt of hydroxymethane
sulfinic acid (available under the trade designation RONGALIT from
BASF, Ludwigshafen, Germany). All of these initiators and the
emulsifiers have an optimum pH-range where they show most
efficiency. For this reason, buffers are typically used. The
buffers include phosphate, acetate, or carbonate buffers, or any
other acid or base such as ammonia or alkali metal hydroxides. The
concentration range for the initiators and buffers can vary from
0.05% by weight to 5% by weight, based on the aqueous
polymerization medium.
Removal of Ions
[0030] The removal of the ions from the corresponding dispersions
used during polymerization is preferably achieved by using cation
and anion exchangers. It is a preferred way to remove first the
anions (such as perfluorooctanoate, sulfate, chloride, fluoride,
etc.) from the dispersions. The removal of the anions via anion
exchangers is an important step for the following reasons: the
latex particles have a submicroscopic diameter of less than 400 nm;
the latex particles are anionically stabilized in the sense of
colloid chemistry; the anionic stabilization is provided by anionic
endgroups, mostly --COOH and --OSO.sub.3H groups, and by the
adsorbed anionic emulsifier such as PFOA. Such anionically
stabilized dispersions tend to coagulate readily in an anion
exchange bed and thus jam the ion exchange bed. Therefore, the
treatment of an anionically stabilized dispersion with an anion
exchanger is considered to be technically not feasible, in
particular at higher concentrations.
[0031] The impairing or clogging of the anion exchange bed is
already observed at solid contents 1000 times lower than those of
the raw polymer dispersions, i.e., the dispersion after
polymerization. This coagulation does not occur in the presence of
a nonionic emulsifier usually in the range of 0.001 to 3.0% by
weight of solid content as described in International Publication
Nos. WO 99/62830 and WO 99/62858. Nonionic emulsifiers are
described in detail in "Nonionic Surfactants" edited by M. J.
Schick, Marcel Dekker, Inc., New York, 1967.
[0032] The choice of the nonionic emulsifier is not critical. Alkyl
aryl polyethoxy alcohols, alkyl polyethoxy alcohols, or other
nonionic emulsifier may be used. Preferred nonionic surfactants are
alkyl aryl polyethoxy alcohol type such as that available under the
trade designation TRITON X 100 from Rohm & Haas, or alkyl
polyethoxy alcohol type such as that available under the trade
designation GENAPOL X 080 from Clariant GmbH.
[0033] The choice of the ion exchange resin is not very critical.
Usable anion exchange resins include those commercially available
under the trade designations AMBERLITE IRA 402 and AMBERJET 4200
from Rohm and Haas, PUROLITE A 845 from Purolite GmbH, LEWATIT
MP-500 from Bayer AG, and DOWEX 1X-2X series from Dow Chemical.
[0034] The specific basicity of the anion exchanger used is not
very critical. Weakly, medium and strongly basic resins can be
used. Preferably, the ion exchange resin is transformed to the
OH.sup.- form.
[0035] The flow rate is not very critical, standard flow rates can
be used. The flow can be upward or downward. The ion exchange
process can also be carried out as a batch process by mildly
stirring the dispersion with the ion exchange resin in a vessel.
After this treatment the dispersion is isolated by filtration.
[0036] The removal of the anions is preferably carried out with raw
dispersions from the polymerization. Such dispersions generally
have a solid content of 10% by weight to 40% by weight, to which is
added sufficient nonionic emulsifier to provide dispersion
stability and, if necessary, to decrease the solid content to less
than about 20%. In a subsequent step the cations are removed by
using readily available resins like LEWATIT SP 112 (Bayer AG),
preferably in the H.sup.+-form. The use of mixed ion exchange
resins (which have anion and cation exchange groups) is a
possibility, too.
Preparation of Fluoropolymer Latex
[0037] Following removal of the ions, the fluoropolymer is
preferably coagulated from the latex without the addition of ions.
This can be effected by the known freeze-coagulation process as
described in U.S. Pat. No. 5,708,131. During this process the whole
aqueous latex is frozen and the polymer is coagulated. This process
can be performed batchwise or continuously. While the isolated
polymer is already clean some subsequent washing steps with water
may be beneficial.
[0038] Another process for coagulation without the addition of ions
is the so-called mechanical coagulation process, which is disclosed
in U.S. Pat. No. 5,463,021 for fluorothermoplasts. The
fluorothermoplast dispersions are first compressed to pressures up
to 200 bar to 400 bar (2.times.10.sup.7 to 4.times.10.sup.7
Pascals) and then decompressed through nozzles or slits and thereby
the coagulation is achieved. The high pressures are produced by a
so-called homogenizer. This technology does not work for elastomer
dispersions due to clogging and jamming the equipment. As suggested
in DE 100 04 229.5 (filed Feb. 1, 2000) these difficulties can be
overcome by generating high pressures with pressurized gases from
50 bar to 400 bar (5.times.10.sup.6 Pa to 4.times.10.sup.7 Pa). In
contrast to the process disclosed in U.S. Pat. No. 5,463,021 the
coagulation by this technique appears to be brought about by the
rapid expansion of the dissolved gas, preferably via a nozzle. The
preferred gases for use with this process are nitrogen, air, or
CO.sub.2.
[0039] In yet another coagulation process a volatile water-miscible
organic solvent effects the coagulation. The solvent is selected
from the group consisting of alkanols of 1 to 4 carbon atoms and
ketones of 2 or 3 carbon atoms. Such solvents should not have a
significant swelling effect on the polymer to prevent the
coagulated or agglomerated polymer from becoming too sticky and
difficult to process.
[0040] Mechanical and thermal methods for coagulating polymers are
disclosed in U.S. Pat. No. 5,463,021, and EP Pat. Nos. B-0 084 837,
B-0 226 668, and B-0 460 284.
[0041] After being coagulated the fluoropolymer may be dewatered.
One method of dewatering the polymer is by mechanical dewatering.
This process is described in U.S. Pat. No. 4,132,845. The wet
polymers can be dried, usually at a temperature within a range of
110.degree. C., preferably 150.degree. C., to 250.degree. C., in
the presence of a carrier gas like air or nitrogen.
[0042] The elastomers with incorporated polymer fillers can be
prepared by blending the solids as described in EP-B-0-708 797 or
by blending latices or rubbers or both either before ion exchange
treatment or thereafter. The latex blend method ensures the most
uniform distribution of the polymer filler and avoids any
contamination as compared to dry blending. After latex blending,
the blends may be coagulated, dewatered, and dried as described
above.
[0043] It is important to avoid the known coagulation chemicals
like salts such as sodium or magnesium chloride or mineral acids
since especially with regard to fluoroelastomers the coagulated
products tend to be sticky and to clump together. Therefore,
despite thorough washing the dried product still contains
significant amounts of such added coagulation chemicals and of
salts present in the polymerization recipe.
Curable Fluoropolymer Compositions
[0044] The present invention provides fluoropolymer compositions
for coating articles by contacting the article with a coating
composition containing the fluoropolymer and immediately after this
coating step or at some later time optionally the coating will be
cured to yield an article with excellent surface properties. The
invention also provides shaped articles prepared from the
fluoropolymers and especially fluoroelastomers, in the latter case
by subsequent curing of the article.
[0045] A preferred curable fluoropolymer composition includes a
peroxide-curable fluoroelastomer essentially free of ions other
than NH.sub.4.sup.+, H.sup.+ and OH.sup.-, and, based on the
elastomeric polymer less than 5.0 parts per one hundred parts of
fluoropolymer resin (phr) of an organic peroxide, less than 10.0
phr of co-agent, and less than 50 phr of a partially crystalline
fluoropolymer essentially free of ions.
[0046] Another preferred curable fluoropolymer composition includes
a peroxide-curable fluoroelastomer and from 0.5 phr to 3 phr of an
organic peroxide, from I phr to 7 phr of a co-agent, and from 10
phr to 40 phr of a partially crystalline fluoropolymer.
[0047] Yet another preferred curable fluoropolymer composition
includes: a peroxide-curable nitrile group containing
fluoroelastomer essentially free of ions other than NH.sub.4.sup.+,
H.sup.+ and OH.sup.-, and, based on the elastomer polymer, less
than 5 phr (preferably from 0.05 phr to 2 phr) of an ammonia
generating cure system, and less than 50 phr (preferably from 10
phr to 40 phr) of a partially crystalline fluoropolymer essentially
free of such ions.
[0048] For a peroxide-curable fluoroelastomer, then the cure-site
monomer includes the bromine- or iodine- or nitrile-containing
monomers described above. A peroxide-curable fluoroelastomer is
especially useful in a curing composition containing an organic
peroxide, a co-agent and, optionally, a fluoropolymer filler.
[0049] When the peroxide-curable fluoroelastomer contains a nitrile
cure-site monomer, it may be cured by using the techniques
described in U.S. Pat. Nos. 5,677,389, 5,565,512, and 4,281,092,
and International Publication No. WO 00/09603. If the fluoropolymer
contains a nitrile group it is especially useful in a composition
containing an ammonia generating catalyst. See, for example, U.S.
Pat. Nos. 5,677,389 and 5,565,512, and International Publication
No. WO 00/09603.
[0050] Additional cure systems which may be used with copolymers
containing the abovementioned nitrile cure-site monomers include
those described in copending applications with U.S. Pat. No.
60/265,498, 60/233,386 and 60/233,383. These may be used as a
replacement for or in combination with the ammonia generating cure
system discussed above.
[0051] A widely used cure-system comprises polyol compounds in the
presence of onium compounds (U.S. Pat. Nos. 4,233,421, 4,912,171,
and 5,262,490), which adds further ion loadings to the finished
article. For the manufacture of electronic components, such as
semiconductor devices, unusually stringent requirements exist for
sealing compounds. Apparently, fluoroelastomers cured by known
processes cannot meet such requirements.
[0052] The peroxide-curable elastomers are cured by a free radical
process. A curable composition includes a fluoropolymer and a
peroxide to generate free radicals at the desirable curing
temperatures. A dialkyl peroxide, which decomposes at a temperature
above 50.degree. C., is especially preferred when the composition
is to be processed at elevated temperatures before it is cured. In
many cases one will prefer to use a di-tertiarybutyl peroxide
having a tertiary carbon atom attached to peroxy oxygen. Among the
most useful peroxides of this type are
2,5-dimethyl-2,5-di(tertiarybutylperoxy)-hexyne-3 and
2,5-dimethyl-2,5-di(tertiarybutylperoxy)-hexane. Other peroxides
can be selected from such compounds as dicumyl peroxide, dibenzoyl
peroxide, tertiarybutyl perbenzoate, and
di[1,3-dimethyl-3-(tertiarybutylperoxy)-bu- tyl]carbonate.
[0053] Another material which is usually blended with the
composition before it is made into end products is a co-agent
composed of a polyunsaturated compound that is capable of
cooperating with the peroxide to provide a useful cure. These
crosslinking co-agents can be added in an amount equal to 0.5 to
10%, preferably about 1 to 7%, by weight of the copolymer content,
and may be one or more of the following compounds: triallyl
cyanurate; triallyl isocyanurate; tri(methallyl)-isocyanurate;
tris(diallylamine)-s-triazine; triallyl phosphite; N,N-diallyl
acrylamide; hexaallyl phosphoramide; N,N,N',N'-tetraallyl
terephthalamide, N,N,N',N'-tetraallyl malonamide; trivinyl
isocyanurate; 2,4,6-trivinyl methyltrisiloxane; and
tri(5-norbornene-2-methylene) cyanurate. Particularly useful is
triallyl isocyanurate (see, U.S. Pat. No. 5,077,359).
[0054] As discussed above, inorganic acid acceptors are often added
during the peroxide cure step to improve the heat aging resistance
and thermal stability of the polymer; however, the addition of such
acid acceptors would have a very detrimental effect to the ion
content and extractables of the resulting elastomer composition.
Thus, for the curing of the peroxide-curable fluoroelastomers of
the present invention, with or without polymeric filler, it is not
necessary to add further any kind of acid acceptors for obtaining
excellent cure characteristics and physical properties and articles
with low ion contents.
[0055] In cases where improved compression set is desired, the
addition of organo-onium compounds are beneficial to improve
properties in formulations that do not contain inorganic acid
acceptors; however, the improvement in compression set may be
achieved in the fluoroelastomers even if they are not essentially
free of inorganic acid acceptors and ions different than
NH.sub.4.sup.+, H.sup.+ and OH.sup.-. The organo-onium compounds
can be selected from a large variety of compounds in such a way to
meet the specific requirements of various application fields.
[0056] As noted above, the fluoroelastomers utilized in these
curable compositions not only contain a cure-site monomer, they are
also preferably essentially free from units derived from vinylidene
fluoride units. In achieving this improvement in compression set
the fluoroelastomer is combined with (a) an appropriate curative in
amounts and types such as is described above, optionally (b) a
co-agent for the curative in amounts and types such as is described
above, and (c) an organo-onium in amounts and types such as
described hereinafter.
[0057] Organo-onium compounds represent one class of useful
additives to the fluoroelastomer compositions of the invention.
Suitable organo-onium compounds are known in the art, generally as
vulcanization accelerators for the elastomers cured by
dihydroxy-containing curing agents. As it is known, an organo-onium
is the conjugate acid of a suitable Lewis-base (e.g., phosphine,
amine, ether, and sulfide) and can be formed by reacting said
Lewis-base with a suitable alkylating agent (e.g., an alkyl halide
or aryl halide). The organo-onium compounds contain at least one
heteroatom such as N, P, S, or O bonded to organic or inorganic
moieties. Preferably, they do not include fluorine atoms (i.e.,
they are non-fluorine-containing organo-oniums). One particularly
useful class of the quaternary onium compounds broadly comprises
relatively positive and negative ions wherein phosphorus and
nitrogen generally comprise the central atom of the positive ion
and the negative ion may be an organic or inorganic anion (e.g.,
halide, sulfate, acetate, phosphate, hydroxide, alkoxide,
phenoxide).
[0058] Organo-onium compounds, preferably, non-fluorine-containing
organo-onium compounds, suitable for use in the compositions of the
present invention are described in U.S. Pat. Nos. 4,233,421;
4,912,171; and 5,262,490. Examples include triphenylbenyl
phosphonium chloride, tributyl alkyl phosphonium chloride, tributyl
benzyl ammonium chloride, tetrabutyl ammonium bromide, and
triarylsulfonium chloride. Another class of organo-onium compounds
are represented by the following formula: 1
[0059] wherein
[0060] Q is nitrogen or phosphorus;
[0061] Z is a hydrogen atom or is a substituted or unsubstituted,
cyclic or acyclic alkyl group having from 4 to about 20 carbon
atoms that is terminated with a group of the formula --COOA where A
is a hydrogen atom or is a NH.sub.4.sup.+-cation or Z is a group of
the formula CY.sub.2-COOR' where Y is a hydrogen or halogen atom,
or is a substituted or unsubstituted alkyl or aryl group having
from 1 to about 6 carbon atoms that may optionally contain one or
more catenary heteroatoms and where R' is a hydrogen atom, a
NH.sub.4.sup.+-cation, an alkyl group, or is an acyclic anhydride,
e.g. a group of the formula --COR where R is an alkyl group or is a
group that itself contains organo-onium (i.e. giving a
bis-organo-onium); preferably R' is hydrogen; Z may also be a
substituted or unsubstituted, cyclic or acyclic alkyl group having
from 4 to about 20 carbon atoms that is terminated with a group of
the formula --COOA where A is a hydrogen atom or is a
NH.sub.4.sup.+-cation;
[0062] R.sup.1, R.sup.2 and R.sup.3 are each, independently, a
hydrogen atom or an alkyl, aryl, alkenyl, or any combination
thereof; each R.sup.1, R.sup.2 and R.sup.3 can be substituted with
chlorine, fluorine, bromine, cyano, --OR" or --COOR" where R" is a
C.sub.1 to C.sub.20 alkyl, aryl, aralkyl, or alkenyl, and any pair
of the R.sup.1, R.sup.2 and R.sup.3 groups can be connected with
each other and with Q to form a heterocyclic ring; one or more of
the R.sup.1, R.sup.2 and R.sup.3 groups may also be a group of the
formula Z where Z is as defined above;
[0063] x is an organic or inorganic anion (e.g. halide, sulfate,
acetate, phosphate, phosphonate, hydroxide, alkoxide, phenoxide or
bisphenoxide); and
[0064] n is a number equal to the valence of the anion X.
[0065] Also useful as additives to the fluorinated elastomeric
composition are phosphates, phosphine oxides, and amine oxides.
These compounds include, for example, alkyl and aryl phosphate,
triaryl phosphine oxides, trialkyl phosphine oxide, triarylamine
oxide and trialkyl amine oxide. Such compounds include those of the
formula PR.sub.3O and NR.sub.3O where each R substituent is,
independently, a linear or branched alkyl or aryl group.
[0066] Nitrile-containing polymers may be cured by a catalytic
interaction of alkyl tin compounds with the nitrile group, thereby
creating a triazine crosslinked structure ("Modern Fluoropolymers",
High Performance Polymers for Diverse Applications, edited by John
Scheirs, John Wiley & Sons (1997), especially page 351). The
addition of tin compounds, however, also detrimental to the ion
level of the elastomer. It is an aspect of the invention to
preferably cure the purified nitrile elastomer blends in the
presence of ammonia-generating compounds that are solid or liquid
at ambient conditions and generate ammonia under curing conditions.
Such compounds include, for example, hexamethylene tetramine
(urotropin), dicyan diamid, and substituted and unsubstituted
triazine derivatives represented by the formula: 2
[0067] wherein R is a hydrogen or a substituted or unsubstituted
alkyl, aryl or aralkyl group having from 1 to about 20 carbon
atoms. Specific useful triazine derivatives include
hexahydro-1,3,5-s-triazine and acetaldehyde ammonia trimer.
[0068] Objects and advantages of this invention are further
illustrated by the following examples, but the particular materials
and amounts thereof recited in these examples, as well as other
conditions and details, should not be construed to unduly limit
this invention.
Experimental Section
Description of Materials Used
[0069] Anionic exchange resin, AMBERLITE IRA 402 (chloride form)
was supplied by Rohm and Haas. The resin was put into the OH-form
with a 5% NaOH solution. After the elution of the NaOH solution,
the column is flushed with deionized water (DI).
[0070] Cationic exchange resin, LEWATIT SP 112 (NH.sub.4.sup.+
form) was supplied by Bayer AG. It was put into the H.sup.+-form by
an aqueous mineral acid such as sulfuric or hydrochloric acid.
After treatment of the resin with the acid solution the column is
rinsed with excess DI.
Dispersion Preparation
[0071] The fluoroelastomer and/or the partially crystalline
fluoroplastic dispersion were prepared separately by emulsion
polymerization. The desired mixtures thereof were prepared by
blending the thus obtained dispersions. The solids content was
adjusted to 20%. The requested amount of a nonionic surfactant is
added in the form of a diluted solution. Practical levels of
nonionic surfactant are in the range of 10 to 30,000 ppm of
surfactant based on total weight of the dispersion mixture.
Preferred ranges are from 10 to 100 ppm. Typical nonionic
surfactants are, for example TRITON 100 X or GENAPOL X 080.
Column Ion Exchange Process
[0072] The cationic and anionic exchange processes are similar. The
polymer latex is ion exchanged by passing the dispersion through a
column packed with the desired exchange resin (dimension of the
column: diameter 6 cm, height 30 cm). The latex can be delivered to
the column by any means typical for a chromatographic procedure,
e.g. gravity feed, static siphon or an automatic pumping system.
The particular method used to pass the dispersion through the
column is not critical. The elution rate should not exceed 3 times
the bed volume/hour.
Analytical Test Methods
[0073] PFOA concentrations were determined from dispersion samples
taken before and after ion exchange. The PFOA level was determined
by gas chromatography according to standard methods (WO-A-99/62830
and WO-A-99/62858). The concentrations of F, Cl, Br,
SO.sub.4.sup.2, PO.sub.4.sup.3- were determined by ion
chromatography of the "mother liquor" which is the particle free
aqueous phase of the dispersion as obtained by freeze coagulation.
The cation contents of the samples were determined by ion
conductive plasma (ICP) of the polymer samples. Samples were
treated with HNO.sub.3 followed by pyrolysis at 550.degree. C. for
10 minutes in a sealed pyrolysis bomb before subjecting them to
ICP.
Test Methods
[0074] In the following examples, indicated results were obtained
using the following test methods:
[0075] Press-cure samples. Unless otherwise noted,
150.times.150.times.2.0 mm sheets were prepared by pressing at
about 6.9 Mega Pascals (MPa) for 10 minutes at 177.degree. C. for
measuring physical properties.
[0076] Post-cure samples, unless otherwise noted, were prepared by
placing a press-cured sample in a circulating air oven. The oven
was maintained at 232.degree. C. and the samples treated for 16
hours.
[0077] Tensile strength at break, elongation at break, and modulus
at 100% elongation were determined using ASTM D 412-92 on samples
cut from the press-cure or post-cure sheet with ASTM Die D. Units
reported in MPa.
[0078] Hardness was determined using ASTM D 2240-85 Method A with a
Type A-2 Shore Durometer.
[0079] Compression set was determined on O-rings using ASTM 395-89
Method B. The O-rings had a cross-section thickness of 3.5 mm
(0.139 inch). After post-curing, the O-rings were compressed for 70
hours at 200.degree. C. Results are reported as a percentage of
permanent set. The melt flow index (MFI) was determined according
to ISO 12086. Mooney viscosities were measured according to ASTM
D-1646. All percentages are by weight unless otherwise stated.
Procedure for Anionic Exchange
[0080] Five kilograms (kg) of a dispersion with a solids content of
28.5% is diluted to 18% solids with deionized water (DI).
Seventy-five grams (g) of a 20% solution of GENAPOL X 080 in DI is
added to this mixture and stirred slowly over night. The dispersion
is subjected to anionic exchange by passing the dispersion through
a 600 ml column packed with 400 ml of the anionic exchange resin
prepared as described above. The elution rate is adjusted to 600 ml
dispersion/hour.
Procedure for Cationic Exchange
[0081] The dispersion after anionic exchange is treated in a
similar manner with 400 ml of the cationic exchange resin. The
polymer is isolated from the dispersion by freeze coagulation.
EXAMPLES 1 to 3
[0082] These samples demonstrate the purity of peroxide cured
samples for different compositions with respect to the elastomer
and the use of partially crystalline fluoropolymer fillers. The
materials were purified according to the Anionic and Cationic
exchange procedures as described above. The resins were recovered
by freeze coagulation. Table 1 identifies the formulations used for
the curing with and without organo-onium compounds and the curing
performance. Table 2 lists some extraction datas of the cured
materials and shows a very low content of extractible ions.
Example 1
[0083] Terpolymer of 31% VF.sub.2, 37% HFP, 31% TFE, 1%
bromotrifluoroethylene (BTFE), Mooney viscosity ML 1+10/121.degree.
C.=70.
Example 2
[0084] Mixture of 80% of a terpolymer from Example 1 and 20% of the
PFA bipolymer (96% TFE, 4% PPVE), MFI 372.degree. C., 5 kg=2.2 g/10
min.
Example 3
[0085] Mixture of 80% of an elastomer from Example 1 and 20% of a
terpolymer: 20% HFP, 63% TFE, 17% ET, MFI 297.degree. C., 5 kg=10.5
g/10 min.
[0086] Table 1: Compound formulation of ultra-clean materials and
curing performance (all values expressed as parts per hundred parts
of rubber (pphr))
1TABLE 1 Compound formulation of ultra-clean materials and curing
performance (all values expressed as parts per hundred parts of
rubber (pphr)) Example designation 6(a) 6(b) 7(a) 7(b) 10 Pphr
(rubber) 100 100 125 125 125 Compound formulation On1 0.75 0.75 On2
1.5 Triallyliso- 3.0 3.0 3.0 3.0 3.0 cyanurate 2,5-dimethyl-2,5-
1.25 1.25 1.25 1.25 1.25 bis (tertiarybutyl- peroxy) hexane Cure
characteristics MDR 177.degree. C. 0.5.degree. Arc ML 0.67 0.67
1.73 1.47 1.17 MH 6.00 6.91 6.47 9.83 8.61 Ts-2 0.96 0.83 1.12 0.67
1.53 Ts-50 1.04 0.95 1.62 0.83 1.63 Ts-90 2.20 1.97 2.83 1.77 3.14
Compression set 46.7 20.9 39.4 24.8 40.4 70 hours, 200.degree. C.,
3.5 mm (0.139 inch) O-rings
[0087] All compositions contain 100 parts of elastomer, "125 parts"
means 100 parts of elastomer+25 parts of filler.
[0088] (a) means compositions without and (b) with onium salt On1
or On2.
[0089] On1 is triphenylbenzyl phosphonium/chloride (neat).
[0090] On2 is Triphenylbenzyl phosphonium/chloride (neat)/methanol
50% solution
[0091] Tests on fluoroelastomer compositions comprising
carbon-bonded hydrogen atoms will also exhibit improved compression
set results with the addition of organo-onium compounds, even for
fluoroelastomers essentially free from vinylidene fluoride.
[0092] Table 2: Extraction data in ng/g of cured samples in
ultra-pure water. Leaching volume: 250 ml, sample weight: 10 g
cut-outs of sheets of 2 mm thickness, leaching time: 14 days at
85.degree. C.
2TABLE 2 Extraction data in ng/g of cured samples in ultra-pure
water. Leaching volume: 250 ml, sample weight: 10 g cut-outs of
sheets of 2 mm thickness, leaching time: 14 days at 85.degree. C.
Example designation 1(a) 1(b) 2(a) 2(b) Cations: *) Potassium 10 10
5 5 Sodium 20 30 15 5 Anions: Fluoride 150 100 85 100 Chloride 5 20
10 20 Bromide 25 30 10 20 *) Al, Ca, Co, Cu, Fe, Mg, Ni, Zn, Sn,
NH.sub.4.sup.+are below detection limits.
EXAMPLES 4-6
[0093] Copolymers with the following compositions were used:
[0094] Example 4: Copolymer of 75 wt % TFE, 24 wt % Propylene and 1
wt % bromotrifluoroethylene(BTFE), Mooney viscosity (ML 1+10 at
121.degree. C.) of 68;
[0095] Example 5: Terpolymer of 24% TFE, 42% HFP, 33% VF.sub.2 and
1% BTFE, Mooney viscosity (ML 1+10 at 121.degree. C.) of 50;
and
[0096] Example 6: Copolymer of 24% TFE, 42% HFP, 33% VF.sub.2 and
1% bromodifluoroethylene, Mooney viscosity (ML 1+10 at 121.degree.
C.) of 50.
[0097] The above copolymers are compounded with the ingredients
listed in Table 3. The formulations used for the curing include
examples with and without organo-onium compounds. Cure rheology
results and compression set for each example are also listed.
3 TABLE 3 Example 4a 4b 5a 5b 6a 6b Fluoroelastomer (parts) 100 100
100 100 100 100 Formulation (listed as parts per hundred parts
rubber-phr) N990 30 30 30 30 30 30 Triallylisocyanurate 2.5 2.5 2.5
2.5 2.5 2.5 2,5-dimethyl-2,5-bis(tertiary 1.25 1.25 1.25 1.25 1.25
1.25 butyl peroxy)hexane Onium I -- 1.5 -- 1.5 -- 1.5 Cure
characteristics MDR 177.degree. C. 0.5.degree. Arc M.sub.L 1.70
1.15 1.02 0.75 1.42 1.13 M.sub.H 4.96 6.17 5.84 12.72 7.53 8.86
t.sub.s2 (min.) 1.27 1.06 0.69 0.59 0.73 0.69 t'50 (min.) 1.50 1.27
0.79 0.83 0.90 0.94 t'90 (min.) 2.65 3.89 2.92 1.95 2.37 2.25
Compression set (%) 56.2 52.4 47.3 40.3 50.6 46.0 70 hours,
200.degree. C., 3.5 mm (0.139 inch) O-rings Onium I = Triphenyl
benzyl phosphonium chloride a = without onium b = with onium
[0098] The complete disclosures of the patents, patent documents,
and publications cited herein are incorporated by reference in
their entirety as if each were individually incorporated. Various
modifications and alterations to this invention will become
apparent to those skilled in the art without departing from the
scope and spirit of this invention. It should be understood that
this invention is not intended to be unduly limited by the
illustrative embodiments and examples set forth herein and that
such examples and embodiments are presented by way of example only
with the scope of the invention intended to be limited only by the
claims set forth herein as follows.
* * * * *